Investigation of Heat Transfer and Pressure Drop for R744 in a Horizontal Smooth Tube of R744/R404A Hybrid Cascade Refrigeration System—Part 2: Low-Temperature Region

Min-Ju Jeon ()
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Min-Ju Jeon: Department of Refrigeration and Air-Conditioning Engineering, College of Engineering, Chonnam National University, 50, Daehak-ro, Yeosu, Jeonnam 59626, Republic of Korea

Energies, 2023, vol. 16, issue 13, 1-20

Abstract: This paper studies the evaporative heat transfer characteristics of R744 at low temperatures in a horizontal smooth tube as a cascade refrigeration system (CRS) among hybrid cascade refrigeration systems (HCRSs). There is a lack of research on the low-temperature evaporative heat transfer characteristics of R744 under the operating conditions of evaporators used in actual CRSs used in supermarkets. Therefore, this study aims to provide basic data on the evaporative heat transfer characteristics of R744 in the evaporators of refrigerators used in supermarkets. The tube used in the evaporation experiment conducted herein was a smooth horizontal copper tube with an inner diameter and length of 11.46 mm and 8000 mm, respectively. The experimental parameters were as follows: heat fluxes of 11.8–21.3 kW/m 2 , mass fluxes of 76.3–175.1 kg/(m 2 ·s), and saturation temperatures of −49.8–−30.2 °C. The main results are summarized as follows: the evaporative heat transfer coefficient of R744 can be predicted well by using the correlation formula of Chen at the evaporation temperature of −40 °C in the CRS.

Keywords: smooth horizontal tube; evaporation heat transfer; evaporative heat transfer; flow boiling; heat transfer; heat transfer coefficient; pressure drop; low temperature; dry-out; flow pattern map; flow regimes; R744 (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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